Objectives of this kind are known as projection objectives for use in microlithography wherein the radiation lies in the deep ultraviolet range (wavelengths of 248 nm, 193 nm and others). An example of such a projection objective is presented in U.S. Pat. No. 5,402,226 and in U.S. patent application Ser. No. 08/583,025, filed Jan. 19, 1996, both of which are incorporated herein by reference.
European patent publication 0,465,882 (corresponding to U.S. patent application Ser. No. 07/551,116, filed Jul. 11, 1990) also discloses a high resolution reduction catadioptric lens.
U.S. Pat. No. 5,251,070 shows a catadioptric reduction projection optical system in FIG. 4 thereof wherein the numerical aperture is 0.4 so that the requirements on this objective are overall relaxed. The angle of the marginal ray increases from the object (that is, from the reticle) to the beamsplitter and mirror.
U.S. Pat. No. 5,402,226 provides a significantly reducing imaging scale of the concave mirror, that is, less than 0.3 (in the embodiment shown, the imaging scale is less than 0.14) for the case where the objective provides a reduction by a factor of 4. In the embodiment of FIG. 2 or FIG. 3 and in Table 2, the sine of the marginal ray angle at the reticle is 0.145 with a numerical aperture of 0.58. After the first lens group and at a possible location for the folding mirror, the numerical aperture is approximately 0.13 and, after the second lens group (that is, at the input of the beamsplitter), the numerical aperture is 0.060.
European patent publication 0,608,572 (corresponds to U.S. patent application Ser. No. 08/009,284, filed Jan. 26, 1993, and 08/134,505, filed Oct. 8, 1993) discloses a catadioptric optical reduction system. In this publication, the lens group lying forward of the beamsplitter cube and the lens group lying forward of the concave mirror both have "negative power". Accordingly, the local numerical aperture (which is the same as the sine of the angle of the marginal ray) is increased. The forward-mounted lens groups are so configured that they image the entry pupil from infinity into the system diaphragm at the concave mirror. With this measure, the beam cross section at the beamsplitter input can, inter alia, be held low. In this way, one obtains an advantageously small beamsplitter cube even for a high numerical aperture (0.7) of the objective.